Process of puffing tobacco stems by radiant energy



United States Patent 3,409,022 PROCESS OF PUFFING TOBACCO STEMS BY RADIANT ENERGY Roger Zygmuut de la Burd, Richmond, Va., assignor to Philip Morris Incorporated, New York, N.Y., a corporation of Virginia No Drawing. Filed Dec. 17, 1965, Ser. No. 514,667 1 Claim. (Cl. 131-121) ABSTRACT OF THE DISCLOSURE This disclosure involves the exposure of tobacco stems, containing at least 4% to 23% moisture by weight, to a radiant energy source having a temperature of from 190 C. to 300 C., preferably 140-170 C., at a pressure of from 20 mm. Hg to slightly greater than atmospheric pressure for from seconds to minutes and at a distance from the radiant energy source of from one to 10 inches so as to induce puffing or expansion thereof there by rendering such stems suitable for use in smoking articles without further treatment.

This invention relates to a method of making puffed tobacco stems. More particularly, the invention relates to a method for treating stems and large veins or midribs which have been removed from tobacco leaves to convert the stems into a form in which they are available for use in smoking articles.

Tobacco stems have generally created problems in the tobacco industry and before tobacco could be utilized for the production of smoking articles, such as cigars, cigarettes, cigarillos and the like, it has been the practice to remove the stems and veins which form a part of tobacco leaves from the tobacco leaves. This removal has been accomplished by the use of threshing machines which break up the leaves and remove the stems and most of the veins from the leaves or by means of steaming machines which strip the stems from the tobacco leaves.

The stems and large veins which have been removed from the tobacco leaves have not found a ready use in the tobacco industry and many attempts have been made to convert the stems and larger veins (all of which will hereinafter be referred to as stems) to useful products. For example attempts have been made to incorporate stems in cigars and cigarettes by crushing the stems and thereafter steaming and rolling the stems prior to their use in the cigarette or cigar filler. It has been found, however, that the undesirable hard wood-like characteristics of the stems have not been removed by such treatment and that the stems, when incorporated in the cigarettes or cigars, have been found to result in uneven burning and in a somewhat less desirable flavor. In addition, the use of stems prepared in such a manner has resulted in minute, rigid stem particles, many of which are readily dislodged from the ends of the tobacco products and can be readily detected by the person smoking the tobacco product due to their sharp nature. In addition, some such hard stern pieces have been found to penetrate the paper wrapper of cigarettes or to deform the cigarette or cigar in an undesirable manner.

Another method which has been proposed for the treatment of stems to make them more acceptable in tobacco products has been to subject the stems, while still in the tobacco leaves, to a fluid pressure which is released to effect the expansion of the stems in the leaves. This method is disclosed in US. Patent No. 2,344,106 to Reed, which issued on Mar. 14, 1944. It has been found, however, that such a method is difficult to operate, involving the use of pressure equipment and the like and involving the use of steam in order to prepare the product for the 3,409,022 Patented Nov. 5, 1968 expansion step. Additional disadvantages of such a process include internal cell damage to the tobacco product, rupture of the epidermis and down-grading of the product resulting from the introduction of gases into the leaf. Further, the nature of such a process dictates that stems be treated batchwise so that production line methods cannot be employed.

Another attempt which has been made to treat tobacco stems or tobacco leaves containing stems has involved the use of a high frequency electrostatic field in order to expand the stems. This process is disclosed in US. Patent No. 2,739,599 to Abbott, which issued on Mar. 27, 1956. Such a process, while having the theoretical capability to eliminate some of the disadvantages of the crushing and steaming technique and of the pressure technique discussed above, has been found to have its own disadvantages. For example, when such a process is employed for the treatment of stems while still in the leaf, it has been found that the leaf itself is sometimes damaged, due to arcing between the plates which are employed to generate the high frequency electrostatic field. It is believed that such arcing occurs at areas in the leaf having a high mineral content. High spots in the leaf are also believed to be a cause of such arcing. The occurrence of such arcing has been found to require frequent machine shutdowns when such a process is employed. Another disadvantage of such a process results due to the fact that tobacco leaves vary in moisture content. Thus, an uneven absorption of energy from the dielectric field results and a non-uniform tobacco product is produced. To overcome this disadvantage, it is necessary to employ expensive moisture control of the stem prior to utilizing the stem in such a process. Another disadvantage of such a process results in the fact that burning of the product could occur in portions of the stem which, due to their highly compacted nature, could absorb more energy. Such burned portions are brittle and have been found to crumble in the course of later treatment of the stems giving rise to undesirable dusting or formation of dust. Thus, prior to the present invention no completely satisfactory process has been found for the treatment of tobacco stems.

The present invention is an improvement over the above-described methods for utilizing tobacco stems and provides a commercially practical method ,for utilizing stems which have been removed from tobacco leavesby treating said stems in a manner such that they can be directly incorporated in a tobacco product, such as a cigarette or a cigar.

The invention comprises a process whereby tobacco stems are exposed to a source of radiant energy under controlled conditions. The process may be abatch process or may be a continuous process which is readily adaptable to production line techniques by carrying the stems on a conveyor belt in a manner such that they are exposed to a desired amount of radiant energy for a desired period of time past a radiant energy source. A high degree of flexibility is introduced by use of a radiant energy source. Unlike steam or gas expansion processes, radiant processing may be practiced at selected wave lengths, depending on the heat source employed. This allows a measure of control over the rate of heat energy absorption by the stems.

The puffing of tobacco stems can be accomplished by exposing the stems, for example, bright tobacco stems or burley tobacco stems, to a source of radiant energy until the stems have puffed or expanded but not to the point where the stems are burned.

The stems which are to be puffed should preferably have a moisture content of between about 5 and 18% by weight but may have a moisture content of from 4 to the stems is from about 9 to 12% by weight.

The. stems, which may be separated from the tobacco leaves and which may be in whole form or in chopped-up or particulate form, are exposed to a source of radiant energy, which may be a high intensity heat lamp, a muffie furnace, a liquid heat exchanger, a quartz lamp, an infrared lamp, a hot plate or the like, for a period of from about seconds to about minutes or more, depending upon the particular tobacco stems or plant parts involved and the size thereof. The source of radiant energy may, for example, be a lamp such as a 1000 watt quartz lamp placed at a distance of about 1 inch to 10 inches from the stems and must generate enough heat to bring the temperature of the tobacco stems to a level of from about C. to about 240 C. and preferably from about 30 C. to about 190 C.

Pufiing in a mufile furnace or on a hot plate is somewhat less eflicient because of dissipation of heat, lack of adequate controls, direct contact of the heat source with the stems and the inability to utilize such heat sources in a continuous fashion. Exposure to forms of radiant energy such as liquid heat exchangers, quartz lamps and infrared lamps may be accomplished successfully in continuous fashion. The liquids in a heat exchanger can be reheated to the temperature range desired for a particular material. Quartz lamps and infrared lamps have the advantage of emanating selected wave lengths which allows close control of the desired degree of browning of the tobacco.

The process of present invention may be conducted at atmospheric pressure or above or may be conducted at subatmospheric pressures. Subatmospheric pressures of from about 20 mm. Hg are satisfactory for the purposes of this invention. Obviously, the higher or lower pressures may be employed, depending on the nature of the tobacco product being treated and the temperature which is employed.

A particularly preferred method for treating the tobacco stems involves the use of lower temperatures with subatmospheric pressures, a process which can be described as a low heat vacuum process. Such a process is conducted by placing the tobacco stems or plant parts containing stems in an atmosphere maintained at a pressure of from about 20 to 759 mm. Hg and subjecting the stems or other plant parts containing stems to a temperature of from about 140 to 170 C., preferably about 145 to 155 C., for a period of time sufficient to cause the pufiing of the stems, which time may be generally from about 30 seconds to 20 minutes.

The radiant heat process in all its embodiments has considerable advantages over pufiing methods known heretofore. It has been found that the dielectric process discussed earlier does not puff those stems which overlap adjacent stems while a batch was being treated in the electromagnetic field. The radiant process, on the other hand, can be used to puff stems in layers up to several inches in thickness. Because the radiant process effects pufling more slowly, damage to the epidermis noted in prior art processes is eliminated. Further, desirable changes in the chemical composition of the puffed stem can be effectuated using the radiant process. Amino acid, phenol and peptide content decreases. N and other nitrogenous substances are also less prevalent.

Advantageous physical changes are also noted. Although macropore diameter remains unchanged, micropore diameter changes after puffing and new micropores are formed. whose diameter are smaller than those encountered in unpuffed tobacco stems. These physical changes, such as surface expansion and micropore formation, give rise to irnproved'organoleptic properties. One desirable physical change may be used to determine whether and to what extent the stems have puffed. Microscopic analysis shows that the stem expansion takes place in the mesophyll while the lignin remains substantially unchanged. Therefore, the degree of expansion or pufiing in the mesophyllic cells defines the extent to which the stem has puffed. These and other advantages to be developed below, all characterize the invention.

The following examples are illustrative:

EXAMPLE 1 Two 1000 watt G.E. type T quartz lamps were installed above a conveyor belt at a distance of 3 inches from the belt and one 1000 watt quartz lamp of the same type was installed below the belt at a distance of 2 inches. The belt was of brass mesh, a substance which readily passes radiant energy. Bright tobacco stems were exposed to the lamps at high intensity (1000 watts) for 10 seconds and a lower intensity (750 watts) for 42 seconds. The longer stems puffed more readily than the short stems. Small splinters and fine particles did not puff at all.

EXAMPLE 2 Mixed bright stems preconditioned at 24 C. and 60% relative humidity were subjected to radiant energy from two 1000 watt G.E. type T quartz lamps placed 2 inches above a conveyor belt. The stems were placed on the belt and carried under the lamps at various belt speeds and heat intensities. The temperature on the surface of the belt was measured. For a given exposure time, it was found that the stems would begin to puff at a certain temperature but would toast, that is darken rapidly on their surface and begin to flame shortly thereafter, at a somewhat higher temperature. At a belt surface temperature of 350 C. the stems began to puff after 8 seconds and began to toast after 17 seconds; at 325 C., puffing began after 12 seconds and toasting after 25 seconds; at 300 C., puffing began after 20 seconds and toasting after 52 seconds; at 225 C. and 190 C., puffing began after 30 and 44 seconds respectively and no toasting was observed. It appeared that the time required for pufiing and toasting was a function of the temperature of the treatment. Therefore, the temperature of the heat sources determines the exposure time of the stem at that temperature. Below 190 C. the pufiing is quite inefficient. About 300 C. the time interval between puffing and toasting is too short to remove the puffed stems from the heat source before they begin to burn. An optimum temperature lies therefore between 190300 C. Continued experimentation showed that a temperature of 250 C. and an exposure time of 30 to 40 seconds gave the best results. The range of temperatures of the stems while attaining the puffed state was found to be to C.

At the optimum conditions of temperature and time, the product was acceptably puffed and the yields of puffed stems were found to exceed 72%. The extent of volume expansion could, of course, be modified by changing the temperature and exposure conditions. Up to 95% of the sample could be puffed if darkening of stems were permissible. However, the darkened portions were found to be brittle and hence led to dust formation.

EXAMPLE 3 Twenty pounds of mixed bright stems, conditioned to 10.2% moisture, were exposed to radiant heat produced by three 1000 watt G.E. quartz lamps arranged in a reflector above a conveyor belt. The temperature on the surface of the belt was 330 C. and the average exposure time was 22 seconds. The puffed stems were allowed to equilibrate at 60% RH. and 74 F. for a period of 5 days. They were compared with stems puffed by gas or fluid expansion and by high frequency electrostatic energy and compared against control unpuffed stems. The stems puffed by gas or fluid expansion were prepared by exposure to steam. The stems puffed by high frequency electrostatic energy had been placed in a Revelac Model C6C-P 10 kw. dielectric oven for 9 seconds. A sample of ground unputfed control and the ground radiantly puffed stems were subjected to evaluation by an expert panel of 37. Their findings were that the unpuffed control was more like hay, more musty and more sour than the puffed sample. On the other hand, the puffed stems were judged to have more total aroma, and chocolate-like, sweet, and toasted aroma. The stems puffed by liquid or gas expansion and by high frequency electrostatic energy were similar in aroma to unpuffed stems. The same samples were subjected to smoke evaluation by the expert panel. The cigarettes containing puffed stems were judged as milder and more aromatic than the control which was made from unpuffed stems.

EXAMPLE 4 Mixed bright stems were placed in a Freas laboratory vacuum oven where they were exposed to atempcrature of 145 C. for to minutes in a vacuum of approximately 25 mm. Hg. The number of stems puffed was approximately 90 to 95%, quite above the average that was obtained while pufiing at the optimum temperature and time at atmospheric pressure. The exact yield was a function of the temperature in the oven, the pressure being held constant at 25 mm. Hg. At 100 C. only a 20% yield was obtained on the average for 25 trials at 100 C. At 110 C., an average of about 20% of the stems puffed; at 120 C., the average of stems puffed rose to 25%; at 130 C., about 40% puffed; at 140 C. about puffed; at 150 0, about puffed. At temperatures in excess of 155 C., the stems tended to darken excessively and it was concluded that a temperature of about 140 to 150 C. was optimum.

At a vacuum of 6 mm. Hg the following percentage of stems puffed at the given temperatures:

Degrees 0.: Percent putfing (approx) 20 20 24 38 75 90 1 94 Temperature at which stems darken excessively,

In general, stems puffed by this low heat technique were found to be somewhat darker than stems puffed at atmospheric pressure with radiant energy.

EXAMPLE 5 Mixed bright tobacco stems, equilibrated at 10.2% moisture, were exposed for one minute to radiant heat in a mufiie furnace at 350 C. The puffed stems removed from the furnace were immediately examined for moisture content. The moisture of the stems immediately after pufiing was 5.2%. However, if the puffed stems were allowed to stand exposed to air for 20 minutes after completion of puffing, they continued to lose moisture at a very rapid rate. After 20 minutes, the moisture was approximately 4.2%. If the stems were further allowed to equilibrate at 60% RH. and 74 F., they gained moisture slowly until they equilibrated to the moisture content of the unpuifed leaf and stem. The results obtained are summarized in Table 1.

Table 1.Moisture holding properties of stems at 24 C.

Stem moisture Relative humidity, percent: content, percent 55 12 .When the gases evolved on puffing were examined by infrared and mass spectroscopy, substantial amounts of hexane, methyl furan, benzene, Z-butenone, pentenes, isoprene, carbon sulfoxide, acetone, butadienes, methyl chloride, acetaldehyde, propene, and methanol were found. As the presence of these products is undesirable in the stem, it is concluded that radiant processing is useful in eliminating unwanted chemicals from the stem.

Radiantly puffed stems were examined for changes in surface area and pore size distribution by the BET method (Brownon, Emmett and Teller, J. Amer. Chem. Soc., vol. 60, p. 309, 1938). The data indicated that the microsurface increased by more than 100% and that pufiing changed the distribution of pore size. New micropores were created, some with diameters smaller than they existed in the original stem. The macropores remained relatively unchanged. Total BET area before pufling Was 18.30 m. g. and after pufling was 41.20 m. g. Before pufling the pore size was 18.00 A. and after pufling was 15.00 A. Before puffing the smallest pore size found was 8.00 A. and after pufling, 7.00 A.

EXAMPLE 6 Mixed bright tobacco stems were equilibrated to approximately 10.2% moisture by exposing them for three days to 74 F. and 60% RH.

Six samples of the conditioned stems were exposed to radiant heat in a mufile furnace manufactured by Thermo Electric Manufacturing Company, Dubuque, Iowa. Each sample contained approximately 250 g. of stems, and was exposed to a range of temperatures for varying lengths of time. A two minute exposure at 400 C. expanded the structure but burned the stems. Exposure at 350 C. for one minute produced puffed stems with a certain degree of toasting, and the aroma of the stems was judged by a panel of experts as more intense and aromatic than the unpuffed stem. The same effect was observed on the samples exposed for 30 seconds at 350 C. but the degree of toasting was not as pronounced. Pufling was also observed with stems exposed for 15 seconds, but the color of the resulting stems was lighter and the structure had expanded mostly in the outer layer of the stems.

I claim:

1. The method of treating tobacco stems having a moisture content of approximately 4% to 23% (at least 4%) by weight which comprises bringing the tobacco stems into proximity With a source of radiant energy having a temperature of from about 140 C. to C. while at a subatmospheric pressure above 10 mm. Hg to about 30 mm. Hg for from about 10 seconds to 20 minutes so as to cause puffing of the stems.

References Cited UNITED STATES PATENTS 2,124,012 7/1938 Smith. 2,344,106 3/1944 Reed l31140 2,739,599 3/1956 Abbott 131140 1,104,990 7/1914 Harding 9981 2,653,093 9/ 1953 Baer 13114O X FOREIGN PATENTS 947,280 1/ 1964 Great Britain.

MELVIN D. REIN, Primary Examiner. 

